Treatment of sour petroleum distillates



Patented July 10, 1951 TREATMENT OF SOUR PETROLEUM DISTILLATES Albert J.Shmidl, Houston, Tex., assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N.J., a corporation of Delaware No Drawing. Application February 19, 1949,Serial No. 77,443

9 Claims. 1

The present invention is directed to a method for treating sourpetroleum distillates. More particularly, the invention is directed tothe sweetening of sour petroleum distillates in the 2 small amounts ofcatalytic reagents are employed. In the foregoing description of theprior art, it will be seen that the prior art workers added compoundssuch as phenols and certain amines presence of an alkali metal hydroxideand a mild b to the alkaline solutions which were employed to oxidizingagent. treat sour petroleum distillates. I have now Prior to the presentinvention, it has been found that, in distinction to the prior artworkknown to treat sour petroleum distillates with ers, improved resultsmay be obtained by adding aqueous alkaline solutions, such as solutionsof catalytic amounts of an alcoholic amine to the alkali metalhydroxide, to remove hydrogen sulsour petroleum distillate. Therefore,in accordfide and other acidic bodies, following which the ance with thepresent invention the foregoing sour distillates were treated withsodium plumbite objects may be achieved'by adding to sour petrosolutionto convert deleterious sulfur compounds leum distillates small amountsof alkanol amines to compounds which are largely innocuous. This andthen contacting the sour distillates containand other prior artprocesses relied on the addi-' ing the alkanol amine with a very smallcatalytic 'tion of sulfur to cause the conversion of the quantity ofasolutionof an alkali metal hydroxide sulfur compounds from mercaptansto disulfides. while maintaining in contact therewith a mild Otherprocesses convert the undesirable comoxidizing agent. pounds by means oflead sulfide'which is then Accordingly, it may be seen that the presentseparated from the gasoline. Frequently, the invention may be describedbriefly as involving separation of lead sulfide from the gasoline wastreating a sour petroleum distillate boiling in the not complete, andconsequently, some was carried range from about 50 to 750 F. bycontacting the over into storage, which was disadvantageous. distillatewith a solution of an alkali metal hy- Furthermore, the addition ofsulfur to gasoline droxide while maintaining in the sour distillatefrequently impaired the octane number level of a catalytic amount of analkanol amine and the gasoline since it is well known that sulfur andadding to the contacted mixture a mild oxidizing its compounds affectgasoline detrimentally. agent suflicient to sweeten said distillate,follow- Efforts have been made in the prior art to ing which the alkalimetal hydroxide is separated remedy this situation, and the workers inthe from the contacted distillate. field have turned to adding certaincompounds, The alkanol amines employed in the practice 'such as phenolsand amines, to alkaline solutions, of the present invention include theethanol such as sodium hydroxide, to cause conversion amines such asmono-, di, and triethanol amine, through an oxidation mechanism of thedelethe mono-, di-, and tripropanol and butanol terious compounds in thesour naphtha. Freamines and the higher members of the same quently suchexpedients are unsatisfactory in not homologous series. The compoundsused in the completely sweetening the product, and an afterpresentinvention have the general structural treatment, by one of the wellknown procedures, formula NH3-r(CyH2yQH) a: where N is the amine becomesnecessary. nitrogen, as is an integer from 1 to 3,, and y is an From theforegoing discussion of the prior art, integer from 1 to 18, inclusive.it will be seen that the petroleum refining indus- 40 These compoundsmay be employed in try has been faced with a problem of convertingamounts, based on the naphtha, varying from deleterious sulfur compoundspresent in petro- 0.001 to 1.0 per cent by volume, with a preferred leumdistillates to those which do not detrimenrange from about 0.01 to 0.15per cent by volume. tally affect the quality of the product. It is to beemphasized that the specified amount It is, therefore, the main objectof the present of the alkanol amines should be added to the invention toprovide a treating process in which naphtha and not to the alkalinesolution. These improved results are obtained in converting obcompoundsare employed generally in a small jectionable sulfur compoundstoharmless bodies. amount effective to sweeten the naphtha in ac- Anotherobject of the present invention is to cordance with the presentinvention and may provide an improved sweetening process in which exerta catalytic action on the sweetening operaan active material is added tothe petroleum distion. 7 r tillate being sweetened to catalyze theconversion The alkaline solution employed in the present of deterioussulfur compounds. invention should be a solution of an alkali metalAnother object of the present invention is to hydroxide. Preferably thesolution should be provide an improved sweetening process in which anaqueous solution having a Baum gravity 3 in the range from about 30 to50 B. but solutions of lower strengths may be used under someconditions. For example, a 40 B. aqueous solution of sodium hydroxidegives satisfactory results.

The alkali metal hydroxide may be lithium, sodium, or potassiumhydroxide, but sodium hydroxide will be preferred on account of itsavailability.

The temperature at which the treating operation is conducted willusually be atmospheric temperature and may range from about 60 F. up toabout 120 F., although higher temperatures up to 200 F. may be used. Apreferred temperture range will be from about 70 to about 95 F.Satisfactory results have been obtained at atmospheric temperaturesencountered in the Texas Gulf Coast area.

The present invention will be further illustrated by the followingspecific example:

EXAMPLE I A portion of a hydrogen sulfide free refined kerosene, whichwas a solvent raffinate having a copper number of 50 and a Saybolt colorof 20, was divided into two parts. To one part was added 0.05% by volumeof triethanol amine and the -stock was then contacted with 5% by volumeof 40 B. sodium hydroxide solution in the presence of three times thetheoretical amount of oxygen required to sweeten, employing two minutesagitation in an agitator equipped with paddles operating at 1200revolutions per minute. The second portion was contacted with 5% byvolume, based on the kerosene, of B. sodium hydroxide solution to whichhad been added 0.05% by volume, based on the kerosene, of triethanolamine. The kerosene was then contacted with the sodium hydroxidesolution of triethanol amine in the presence of three times thetheorectical amount of oxygen for two minutes under violent agitation inan agitator equipped with paddles, operating at 1200 revolutions perminute. The sodium hydroxide solution was separated from each of the twotreated portions of the kerosene and the copper number and color of thetreated kerosenes determined. The data in the first column of Table Irepresent the treatment in accordance with the present invention whereasthe data in column 2 represent'prior art techniques where the catalystis added to the sodium hydroxide rather than to the kerosene.

Saybolt Color The data in Table I indicate the markedly superior resultobtained by treatment of the kerosene in accordance with the presentinvention, in which the triethanol amine was added prior to contact withsodium hydroxide in the presence of oxygen over that obtained whentreating in accordance with the prior art methods in which the kerosenewas contacted with a sodium hydroxide solution of triethanol amine. Thecopper number of the naphtha treated according to my invention wasreduced to 32 after contact with sodium .hydroxide, and droppedto after1 hour, to 23 after .3 hours, and to 8 after 24 hours, whereas that ofthe kerosene treated conventionally was substantially unchanged. Ofgreat significance is the color of the kerosene to which triethanolamine had been added and which was treated in accordance with thepresent invention. It will 'be noted that the color after 24 hours was20, the same as the kerosene initially, whereas the color of thekerosene when treated in accordance with conventional techniques haddropped to 12. The color of the kerosene treated in accordance with thepresent invention was even better than that of kerosene treated onlywith 40 B. sodium hydroxide, since the latter dropped to 18 afterstanding in storage for 24 hours.

In the foregoing example, the improvement obtained in the presentinvention has been illustrated by the copper number test. This is a wellknown analytical procedure employed in the petroleum industry. Adescription of the method of test may be found in U. 0. P. LaboratoryTest Methods for Petroleum and Its Products, third edition, page 1-1-61,Universal Oil Products Company, Chicago, 1947. This test is a measure ofthe mercaptan sulfur content of the oil being tested.

(In the practice of the present invention, it is to be understood thatthe sour petroleum distillates employed as feed stocks are free from, ordeficient in catalytic, oxidation promoting *compounds and will notsweeten in contact with a mild oxidizing agent and alkali metalhydroxide. The great majority of petroleum distillates to be sweetenedin general refinery practice will be found to fall in this category.

Although ll'lOt illustrated by the example, one of the particularadvantages of the present nvention resides in the catalytic effect ofthe alkali metal hydroxidesolution. The alkali metal hydroxide appearsto function as a true catalyst since the .small amount used may berecycled to treat large quantities of sour petroleum distillate. A smallamount of the alkali metal hydroxide solution may be entrained in thetreated naphtha, and, therefore, it may be necessary to replace theentrained amount with fresh solution. In short, it is contemplated inthe practice of the present invention that the alkali metal hydroxidesolution will be reused over and over again, since it is notnecessary toregenerate this solution.

The invention has been described and illustrated by employment of a mildoxidizing agent such as oxygen. It is contemplated that mixtures ofoxygen with other gases, such as air, may be employed. It is alsocontemplated that other mild oxidizing agents such as peroxides,permanganates, and the like may be used. For example, a hydrogenperoxide solution may be employed as the mild oxidizing agent.

In practicing the present invention, it is to be understood that thepetroleum distillate maybe subjected to a preliminary treatment forremoval of hydrogen sulfide if the distillatecontains hydrogen sulfide.Such preliminary treatment may include washing with a dilute alkalimetal hydroxide solution or blowing with a free-oxygen containing gassuch as air. If hydrogen sulfide and/or other acidic compounds'arepresent and are not removed, the alkali metal hydroxide solutionemployed as the catalyst may very quickly become'seriously depleted inactivity.

In the practice of the invention, it will be desirable to use an amountof oxygen in excess of the theoretical required to sweeten the sourpetro- :leum distillate. Ordinarily, .an amount of about 5. 300% of thetheoretical amount to sweeten may be employed. However, sweetening inaccordance with the present invention may be obtained with considerablylesser quantities of oxygen. In fact, sweetening may be obtained in somecases by contact with the oxygen present in the treating vessel. It willbe desirable to employ an amount of oxidizing agent at least equivalentto the theoretical amount required to sweeten.

The invention has been described and exemplilied by employment of 0.5 to5.0% by volume of the catalytic alkali metal hydroxide solution. It iscontemplated that as little as 0.1 and as much as by volume, or more, ofthe alkali metal hydroxide solution, based on the sour naphtha, may beemployed. Very good results, however, are obtained with 1% by volume andthis amount will be preferred.

The nature and objects of the present invention having been completelydescribed and illustrated, what I wish to claim as new and useful and tosecure by Letters Patent is:

1. A method for sweetening a sour petroleum distillate containingmercaptans and having a final boiling point no greater than 750 F. whichcomprises adding to said distillate a small but effective catalyticamount no greater than 1% by volume of an alkanol amine and, thenagitating the distillate containing the alkanol amine with a smallamount no more than 5% by volume of a solution of an alkali metalhydroxide while adding a sufficient amount of a mild oxidizing agent toconvert the mercaptans to disulfides and to obtain a sweeteneddistillate.

2. A method in accordance with claim 1 in which the alkanol amine is anethanol amine.

3. A method in accordance with claim 1 in which the alkanol amine is apropanol amine.

4. A method in accordance with claim 1 in which the alkanol amine is abutanol amine.

5. A method in accordance with claim 1 in which the alkanol amine isemployed in an amount in the range from 0.001 to 1.0% by volume of thesour petroleum distillate.

6. A method in accordance with claim 1 in which the mild oxidizing agentis a free-oxygen containing gas.

7. A method for sweetening a sour petroleum distillate containingmercaptans and having a final boiling point no greater than 750 F. whichcomprises adding to said distillate a small but effective catalyticamount no greater than 1% by volume of triethanol amine and thenagitating the distillate containing triethanol amine with no more than5% by volume of an aqueous solution of an alkali metal hydroxide whileadding a sufficient amount of mild oxidizing agent to convert themercaptans to disulfides and to obtain a sweetened distillate.

8. A method for sweetening a sour petroleum distillate containingmercaptans and having a final boiling point no greater than 750 F. whichcomprises adding to said distillate an amount of triethanol amine in therange between 0.001%

and 1.0% based on said distillate and then agitating the distillatecontaining triethanol amine with an effective amount of a sodiumhydroxide solution not over 5% by volume based on the sour distillatewhile adding a sufficient amount of a free oxygen containing gas toconvert the mercaptans to disulfides and to obtain a sweeteneddistillate. I

9. A method for sweetening a sour petroleum distillate containingmercaptans and having a final boiling point no greater than 750 F. whichcomprises adding to said distillate 0.05% by volume of triethanol aminebased on the distillate and then agitating the distillate containingtriethanol amine with 5% by volume based on the sour distillate of anaqueous B. sodium hydroxide solution while adding three times thetheoretical amount of oxygen required to convert the mercaptans todisulfides and to obtain a sweetened distillate.

ALBERT J. SHMIDL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name a Date 2,152,720 Yabrofi Apr. 4, 19392,152,723 Yabrofi Apr. 4, 1939 2,186,398 Yabroff Jan. 9, 1940 2,364,582Davis et a1. Dec. 5, 1944 2,434,868 Sample et al. Jan. 20, 19482,453,067 Happel Nov. 2, 1948

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTIALLATE CONTAININGMERCAPTANS AND HAVING A FINAL BOILING POINT NO GREATER THAN 750* F.WHICH COMPRISES ADDING TO SAID DISTILLATE A SMALL BUT EFFECTIVECATALYTIC AMOUNT NO GREATER THAN 1% BY VOLUME OF AN ALKANOL AMINE AND,THEN AGITATING THE DISTILLATE CONTAINING THE ALKANOL AMINE WITH A SMALLAMOUNT NO MORE THAN 5% BY VOLUME OF A SOLUTION OF AN ALKALI METALHYDROXIDE WHILE ADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TOCONVERT THE MERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENEDDISTILLATE.